This invention relates to regenerative furnaces and their operation and, in particular, to the type of regenerative furnace commonly employed in the manufacture of flat glass. The regenerators used in such furnaces are usually comprised of a gas pervious bed of refractory material, such as a stacked arrangement of bricks sometimes called "checker packing," through which hot exhaust gases are passed during one phase of a firing cycle in order to heat the packing. In the alternate phase of the firing cycle, the flow is reversed and the heat stored in the packing serves to preheat combustion air passing through the regenerator. The regenerators are generally employed in pairs with one on either side of the combustion chamber of the furnace. While one regenerator is absorbing heat from the exhaust gas, the other is heating incoming air.
Because flat glass furnaces typically include a relatively large number of burner ports (usually about 4-8 on each side) spaced several feet apart from one another in a row, the length of a regenerator bed associated therewith usually has a length which is several times greater than its height or width. Because of construction expediencies, the main flue carrying gases to and from each regenerator is usually located at one end of the regenerator. This arrangement unfortunately results in a tendency of gases in portions of the regenerators to flow longitudinally and to by-pass portions of the packing. Hot exhaust gases tend to flow in greater amounts through the portions of the packing near the flue, causing those portions to become hotter than other portions of the packing. This unbalanced condition is aggravated by the fact that the flow of cool, incoming combustion air during the firing phase tends to be biased toward the opposite end of the packing from the flue inlet. As a result, the flue end portion of the packing tends to reach higher peak temperatures as well as maintaining higher minimum temperatures over the firing cycle. Because of the high temperatures, the flue end portion of the packing tends to deteriorate faster than others, thereby shortening furnace life and often acting as a restriction on the operation of a furnace. Furthermore, because the stored heat is concentrated in one portion of the packing, the efficiency with which air is preheated during the firing phase is reduced, thereby reducing the overall thermal efficiency of the furnace. It is an object of the present invention to overcome these disadvantages.
U.S. Pat. No. 1,836,412 and 2,813,708 relate to modifying flow patterns in regenerators. Both employ rigid baffles designed primarily for the purpose of rendering the air flow through the checker packing more uniform during the firing phase. It is not apparent, however, how such arrangements could sufficiently influence flow in the opposite direction through the packing during the exhaust phase to avoid concentrating heat at the flue end of the packing. Moreover, such baffle arrangements could change the gas flow pattern in the space beneath the packing during the exhaust phase, thereby promoting lateral flow of exhaust gases along the space above the packing and then into the packing at the flue end.
Arrangements in which a plurality of flues are provided to distribute gas flows through regenerators are disclosed in U.S. Pat. Nos. 4,174,948; 4,256,173; and 4,257,476. Each of these arrangements requires a substantial rebuilding of the regenerator structure, which may not be practical for existing furnaces and is unsuitable for furnaces that are currently operating continuously. Furthermore, it would be desirable if flow distribution could be achieved without the substantial additional structure required by these arrangements.
In U.S. Pat. Nos. 4,047,560 and 4,088,180 there is shown a movable baffle for diverting air flows during the firing phase of a regenerator. It would be preferred to avoid the use of movable parts, particularly in such a harsh environment where durability can be a problem.
It is also known to provide regenerators with partitions so that each burner port is associated with a corresponding regenerator packing section. While such an arrangement can provide positive control of flow distribution, its use is discouraged by the fact that plugging or collapse of one of the regenerator packing sections can essentially remove a burner port from service, thereby severely crippling the operation of a furnace. For these reasons, it is preferred to employ a unitary, unpartitioned bed of packing in common communication with a plurality of burner ports.